Step Change In Concentration Research Articles

The impact of real-time carbon dioxide awareness on occupant behavior and ventilation rates in student dwellings

Although existing standards typically prescribe fixed ventilation rates, a large portion of the building stock lacks mechanical ventilation systems. Such buildings obtain outdoor air through unintentional infiltration, open windows, and the operation of exhaust fans, which are mainly dependent on user awareness and behavior. This study investigates whether the presence of a simple CO2 meter display can alter user behavior and improve indoor air quality (IAQ) in dwellings. We conducted a two-week monitoring of CO2 concentration, air temperature, and relative humidity in 60 student dwellings (bedrooms and living rooms) in Denmark and Switzerland. During the first week, the CO2 display was concealed, and occupants adhered to their usual routines. In the second week, occupants used the display's visual feedback to enhance IAQ when necessary. Results revealed that over 95% of dwellings witnessed a reduction in median CO2 levels during the second week, both overall and in individual rooms. Furthermore, a descriptive analysis of CO2 concentration step changes exceeding the thresholds of “normal variation” showed an increase in the number of negative step changes, indicating a shift in user behavior. These findings underscore the efficacy ofa display interface providing information on the indoor environment in triggering behavior changes and improving IAQ in dwellings.

Understanding fast adsorption in single-solute breakthrough curves

To design efficient adsorption separations and select high-performing materials, understanding the relationship between adsorption equilibria and the movement of solute waves along the fluid is critical. While approximate-analytical methods are useful to combat nonlinearities in the differential equations and efficiently investigate the myriad of materials, their utility is limited by the lack of a clear physical interpretation and mathematical relationship to well-established models. In this work, we show that the two popular methods can be understood with regular perturbation theory and boundary layer theory in small ɛ, where a dilute solute travels from fluid to solid much faster than along the column. We consider conditions associated with a popular experimental technique used to characterize solute wave movement, where the column is initially at steady state and the fluid concentrations exiting, or breaking through, are time-monitored in response to a step change in inlet concentration. Our transformations and asymptotic analyses illustrate the time scales associated with popular techniques. We generalize their applicability to equilibria possessing inflection points while considering both adsorption and desorption modes. We use numerical simulations to estimate convergence orders of asymptotic approximations of breakthrough concentrations. For the leading-order approximation of regular perturbation theory, rarefaction waves possess positive convergence orders, depending on the extent of nonlinearity, while shock waves do not. Boundary-layer theory affords a more accurate approximation of the breakthrough curve than a shock wave, without guaranteeing a positive convergence order. This lack of positive convergence order is likely due to the evolution of the boundary layer, as illustrated with numerical simulations. An improved understanding of fast adsorption sets the stage for more realistic selection of high-performing materials and design configurations from thousands of available candidates.

A-029 Modeling the Effect of Step Changes in Glucose on %Glycated Albumin vs Time

Abstract Background Glycated albumin (GA) is often referred to as being a reflection of glucose exposure over the past 20–30 days. We examined this premise from a theoretical standpoint using a model for formation of GA and simulation of the effects of step changes in glucose concentration ([G]). Methods A model for glycation of albumin parallels established models for formation of hemoglobin A1c, differing only in characterization of the age distribution for albumin. Probability of survival (P(s)) of albumin at a given age (t) is based on a first-order rate constant (ke) for elimination: P(s) = exp(-ke t) [Eqn.1], where ke = 4.08e-2/d (t(1/2) = 17 d). Probability of glycation (P(g)) at a given age is given by: P(g) = (1-exp(-k[G] t)) [Eqn.2]. There is a simple analytical solution for %GA for constant [G]: %GA = 100(1-w/z), where w = ke and z = (ke+k[G]). k = 9.77e-4/d/(mmol/L) reproduces reference values for %GA [PMID: 29436378], and for which %GA = 2.41(%A1c)-0.004 (r = 0.999, for A1c range = 5%–12%). For non-constant [G], %GA must be determined by simulation of changes in P(g) using Eqn.2, calculated in small time increments, dt. Using dt = 0.01 d, we calculated changes in %GA by simulation as a function of time for two scenarios involving step changes in [G] at time = 0: A. from 10 mmol/L to 15 mmol/L (%GA ultimately moves from 19.3% to 26.4%); B. from 15 mmol/L to 10 mmol/L (%GA ultimately moves from 26.4% to 19.3%). Results Figure shows the fractional transition of %GA between respective starting points and ultimate endpoints vs time for scenarios A and B. In both cases, transition at 30 days was approximately 80% of the ultimate full transition. Conclusions Physiological model-based calculations support that description of %GA as a reflection of [G] over the past 30 days is a very reasonable one under conditions in which [G] has changed.

Study of axial dispersion on several modern structured and random packings

The study investigates the phenomenon of axial dispersion in a packed absorption column, which is known to reduce the efficiency of separation equipment by reducing the mass transfer driving force. The aim of the study is to determine the Bodenstein number, which represents axial dispersion, for five types of modern packings used in the column. The packings used in the study were random packings (NeXRing0.7 and NeXRing1.2) and structured packings (MellaPak350Y, 452Y, and 500Y). The data obtained from dynamic experiments in the form of a response to a step change in tracer substance concentration were compared to a diffusion-type differential equation, which was solved with boundary conditions for a closed system. By measuring the responses at two different packed bed heights and using convolution, the influence of the end effects was eliminated. The lowest axial dispersion was obtained for M452Y, and it is almost twice as low as for M250Y. It was found that the values of the Bodenstein number for standard series of Mellapak type packing (M250Y, M350Y and M500Y) have comparable axial dispersion, especially at low liquid rates. The axial dispersion obtained for random packings is generally higher compared to structured packings. However, compared to other random packings such as Pall rings (25 mm) and Intalox saddles (25 mm), NXR0.7 and NXR1.2 exhibit up to a two-fold reduction in axial dispersion.

Rapid CO2 changes cause oscillations in photosynthesis that implicate PSI acceptor-side limitations.

Oscillations in CO2 assimilation rate and associated fluorescence parameters have been observed alongside the triose phosphate utilization (TPU) limitation of photosynthesis for nearly 50 years. However, the mechanics of these oscillations are poorly understood. Here we utilize the recently developed Dynamic Assimilation Techniques (DAT) for measuring the rate of CO2 assimilation to increase our understanding of what physiological condition is required to cause oscillations. We found that TPU limiting conditions alone were insufficient, and that plants must enter TPU limitation quickly to cause oscillations. We found that ramps of CO2 caused oscillations proportional in strength to the speed of the ramp, and that ramps induce oscillations with worse outcomes than oscillations induced by step change of CO2 concentration. An initial overshoot is caused due to a temporary excess of available phosphate. During the overshoot, the plant out-performs steady state TPU and ribulose 1,5-bisphosphate regeneration limitations of photosynthesis but cannot exceed the rubisco limitation. We performed additional optical measurements which support the role of PSI reduction and oscillations in availability of NADP + and ATP in supporting oscillations.

Potential for bias in effective climate sensitivity from state-dependent energetic imbalance

Abstract. To estimate equilibrium climate sensitivity from a simulation where a step change in carbon dioxide concentrations is imposed, a common approach is to linearly extrapolate temperatures as a function of top-of-atmosphere energetic imbalance to estimate the equilibrium state (“effective climate sensitivity”). In this study, we find that this estimate may be biased in some models due to state-dependent energetic leaks. Using an ensemble of multi-millennial simulations of climate model response to a constant forcing, we estimate equilibrium climate sensitivity through Bayesian calibration of simple climate models which allow for responses from subdecadal to multi-millennial timescales. Results suggest potential biases in effective climate sensitivity in the case of particular models where radiative tendencies imply energetic imbalances which differ between pre-industrial and quadrupled CO2 states, whereas for other models even multi-thousand-year experiments are insufficient to predict the equilibrium state. These biases draw into question the utility of effective climate sensitivity as a metric of warming response to greenhouse gases and underline the requirement for operational climate sensitivity experiments on millennial timescales to better understand committed warming following a stabilization of greenhouse gases.

Characterization of a modified printed optical particle spectrometer for high-frequency and high-precision laboratory and field measurements

Abstract. The printed optical particle spectrometer (POPS) is a lightweight, low-cost instrument for measurements of aerosol number concentrations and size distributions. This work reports on modifications of the Handix Scientific commercial version of the POPS to facilitate its use in multi-instrument aerosol sampling systems. The flow system is modified by replacing the internal pump with a needle valve and a vacuum pump. The instrument is integrated into closed-flow systems by routing the sheath flow from filtered inlet air. A high-precision multichannel analyzer (MCA) card is added to sample the analog pulse signal. The MCA card is polled at 10 Hz frequency using an external data acquisition system and improves upon the count-rate limitation associated with the POPS internal data acquisition system. The times required to change the concentration between 90 % and 10 % and vice versa for a step change in concentration were measured to be 0.17 and 0.41 s at a flow rate of 5 cm3 s−1. This yields a sampling frequency of ∼ 1–2 Hz, below which the amplitude of measured fluctuations is captured with > 70 % efficiency. The modified POPS was integrated into the dual tandem differential mobility analyzer system to explore the coalescence of dimer particles. Results show that the pulse-height response increases upon dimer coalescence. The magnitude of the increase is broadly consistent with the change in light-scattering amplitude predicted by the T-matrix method. It is anticipated that this modified version of the POPS will extend the utilization of the technique for a range of field and laboratory applications.

Influence of the Injection Scheme on the Enhanced Oil Recovery Ability of Heterogeneous Phase Combination Flooding in Mature Waterflooded Reservoirs.

With the maturity of waterflooded reservoirs, owing to serious heterogeneity, the fluid will channel through the thief zone, leading to considerable remaining oil unrecovered in the upswept area. To further enhance oil recovery (EOR) after waterflooding, the heterogeneous phase combination flooding (HPCF) was composed of a polymer, branched-preformed particle gel (B-PPG), and surfactant. For the sake of improving the economic efficiency, the influence of the injection scheme on the EOR of HPCF with an equal chemical agent cost was investigated by sand-pack flooding experiments. Then, visual plate sand-pack model flooding experiments were performed to study the swept area of HPCF under different injection schemes. Results demonstrated that the total EOR of HPCF under different injection schemes ranged from 33.5 to 39.3%. Moreover, the EOR of HPCF under the alternation injection (AI) scheme was the highest, followed by the concentration step change injection (CI) scheme, and that of the simultaneous injection (SI) scheme was the least. The visual flooding experimental results showed that the swept area of HPCF after waterflooding under the AI scheme was higher than that of the SI. Moreover, in view of qualitative analysis of remaining oil distribution, the EOR of AI of HPCF was higher than that of SI, which was consistent with the parallel sand-pack flooding results.

Investigation the impact of using the recess air bio-filter (TBAB) with integrated system of a cyclic 2-recess adsorption/desorption unit for treatment of squander gas streams

In the chemical industry, fluctuations in influent concentrations and shifts in the composition of waste air make biofiltration a challenging technique. As a possible solution to the constraints of biofiltration technology, this research designs and implements an integrated system that includes a cyclic 2-bed adsorption/desorption unit and a trickling bed air biofilter (TBAB). The study's major goal was to keep the TBAB volatile organic compound (VOC) degradation performance stable and consistent over time. The studies were conducted on different TBABs with a single VOC exchange and a biomass control of periodic backwashing. Solvents that are routinely used in paint booths were examined as VOCs. Two aromatic chemicals (styrene and toluene) were investigated, as well as two aliphatic chemicals (methyl ethyl ketone (MEK) and methyl isobutyl ketone) (MIBK). While the production process rotated, our study duplicated VOC emission rotation in certain chemical sectors. When VOCs were switched to aromatics, the biofilter required an apparent re-acclimation period, according to the results. The second phase looked at two different combinations of these VOCs in two separate TBAB trains with a step change in influent concentration. In the third phase, the buffering performance of a cyclic 2-bed adsorption unit was tested for a feeding composition based on an EPA industrial emission report under a square wave of fluctuating conditions. The VOC mixture was treated in the fourth step with an integrated system that includes two cyclic adsorption/desorption beds as well as TBAB. When compared to the control unit, the integrated system was able to achieve high steady performance, according to the studies' findings. Lastly, researchers looked at the microbial communities of the biofilters employed in the VOC interchange and VOC mixing studies. The interchange of VOCs demonstrated a steady transition in microbial diversity. The community structure of VOC mixes demonstrated a significant degree of independence from the component content.

Ligand sensing enhances bacterial flagellar motor output via stator recruitment.

It is well known that flagellated bacteria, such as Escherichia coli, sense chemicals in their environment by a chemoreceptor and relay the signals via a well-characterized signaling pathway to the flagellar motor. It is widely accepted that the signals change the rotation bias of the motor without influencing the motor speed. Here, we present results to the contrary and show that the bacteria is also capable of modulating motor speed on merely sensing a ligand. Step changes in concentration of non-metabolizable ligand cause temporary recruitment of stator units leading to a momentary increase in motor speeds. For metabolizable ligand, the combined effect of sensing and metabolism leads to higher motor speeds for longer durations. Experiments performed with mutant strains delineate the role of metabolism and sensing in the modulation of motor speed and show how speed changes along with changes in bias can significantly enhance response to changes in its environment.

Long-term trends in PM2.5 mass and particle number concentrations in urban air: The impacts of mitigation measures and extreme events due to changing climates

Urbanisation and industrialisation led to the increase of ambient particulate matter (PM) concentration. While subsequent regulations may have resulted in the decrease of some PM matrices, the simultaneous changes in climate affecting local meteorological conditions could also have played a role. To gain an insight into this complex matter, this study investigated the long-term trends of two important matrices, the particle mass (PM2.5) and particle number concentrations (PNC), and the factors that influenced the trends. Mann-Kendall test, Sen’s slope estimator, the generalised additive model, seasonal decomposition of time series by LOESS (locally estimated scatterplot smoothing) and the Buishand range test were applied. Both PM2.5 and PNC showed significant negative monotonic trends (0.03–0.6 μg m−3. yr−1 and 0.40–3.8 × 103 particles. cm−3. yr−1, respectively) except Brisbane (+0.1 μg m−3. yr−1 and +53 particles. cm−3. yr−1, respectively). For the period covered in this study, temperature increased (0.03–0.07 °C.yr−1) in all cities except London; precipitation decreased (0.02–1.4 mm. yr−1) except in Helsinki; and wind speed was reduced in Brisbane and Rochester but increased in Helsinki, London and Augsburg. At the change-points, temperature increase in cold cities influenced PNC while shifts in precipitation and wind speed affected PM2.5. Based on the LOESS trend, extreme events such as dust storms and wildfires resulting from changing climates caused a positive step-change in concentrations, particularly for PM2.5. In contrast, among the mitigation measures, controlling sulphur in fuels caused a negative step-change, especially for PNC. Policies regarding traffic and fleet management (e.g. low emission zones) that were implemented only in certain areas or in a progressive uptake (e.g. Euro emission standards), resulted to gradual reductions in concentrations. Therefore, as this study has clearly shown that PM2.5 and PNC were influenced differently by the impacts of the changing climate and by the mitigation measures, both metrics must be considered in urban air quality management.

Controlling electronic structure of single-layered $${\hbox {HfX}}_{3}$$ ($$\hbox {X=S}$$, Se) trichalcogenides through systematic Zr doping

The electronic structures of $$\hbox {Hf}_{1-x}\hbox {Zr}_{x}\hbox {S}_{3}$$ and $$\hbox {Hf}_{1-x}\hbox {Zr}_{x}\hbox {Se}_{3}$$ trichalcogenides are investigated by first-principles calculation. In particular, step change of Zr concentration is intensively investigated. Our calculations reveal that doping of Zr atoms increase the strength of cohesion between the atoms in $$\hbox {HfX}_ 3$$ (X = S, Se) monolayers, and results in occurring of energetically more stable alloys. In addition, doping of Zr atoms in $$\hbox {HfS}_3$$ causes band gap bowing, which means the curve of band gap values shows quadratic nonlinearities while change from semimetal to semiconductor is observed in $$\hbox {HfSe}_3$$ case. The examined band structures indicate that $$\hbox {Hf}_{1-x}\hbox {Zr}_{x}\hbox {S}_{3}$$ monolayers have very suitable band gap values for water splitting and also their band edge potentials have sufficiently higher or lower positions than the required potential values for the reduction or oxidation potentials.

The Southern Ocean Sea Surface Temperature Response to Ozone Depletion: A Multimodel Comparison

Abstract The effect of the Antarctic ozone hole extends downward from the stratosphere, with clear signatures in surface weather patterns including a positive trend in the southern annular mode (SAM). Several recent studies have used coupled climate models to investigate the impact of these changes on Southern Ocean sea surface temperature (SST), notably motivated by the observed cooling from the late 1970s. Here we examine the robustness of these model results through comparison of both previously published and new simulations. We focus on the calculation of climate response functions (CRFs), transient responses to an instantaneous step change in ozone concentrations. The CRF for most models consists of a rapid cooling of SST followed by a slower warming trend. However, intermodel comparison reveals large uncertainties, such that even the sign of the impact of ozone depletion on historical SST, when reconstructed from the CRF, remains unconstrained. Comparison of these CRFs with SST responses to a hypothetical step change in the SAM, inferred through lagged linear regression, shows broadly similar results. Causes of uncertainty are explored by examining relationships between model climatologies and their CRFs. The intermodel spread in CRFs can be reproduced by varying a single subgrid-scale mixing parameter within a single model. Antarctic sea ice CRFs are also calculated: these do not generally exhibit the two-time-scale behavior of SST, suggesting a complex relationship between the two. Finally, by constraining model climatology–response relationships with observational values, we conclude that ozone depletion is unlikely to have been the primary driver of the observed SST cooling trend.

The effect of sulphates on anaerobic digestion of municipal wastewaters by using UASB reactors at 20 C

The aim of the work on sulphates was to investigate their impact on UASB performance, including the response to step changes in influent concentration. It has been shown that UASB reactors treating municipal-type wastewaters at 20 o C can remove sulphate effectively even at relatively low COD/SO4 ratios and/or high concentrations. In this experiment, therefore the UASB reactors were fed on influent with different sulphate concentrations to establish the effects on key performance parameters. It was used eight 4-litre continuously fed UASB reactors. The effect of sulphate addition on methane production was much greater than on COD removal, the specific methane production and the ratio of actual to theoretical methane produced per g of COD removed showed relatively little effect from influent sulphate concentrations below ~120 mg SO 4 l -1 (COD/SO 4 ratio 5.8), although this may in part have reflected a period of acclimatisation while the population of sulphate-reducing bacteria (SRB) increased.

Development of online microdialysis-mass spectrometry for continuous minimally invasive measurement of soil solution dynamics

The rate that amino acids are removed from the soil solution is poorly known but vitally important. It is possible to determine the time course of soil solution concentrations by extracting soils at different time points after adding labelled compounds, but this approach either lacks sufficient temporal resolution or generates large number of samples that require subsequent offline analysis. The aim of this study was to develop online microdialysis-mass spectrometry to enable the minimally invasive measurement of the time-course of isotope labelled amino acid added to soil. The method was subsequently tested by examining the fate of isotope labelled L- and d-alanine added to sterile and non-sterile soils. One concern with application of microdialysis to soil is if calibrations are affected by inorganic ion composition of the perfusate and the external (soil) solution. Tests showed that the presence/absence of inorganic ions in perfusate and external solution did not affect dialysate concentrations, suggesting that perfusing with an artificial soil solution matching the inorganic ion composition of the external solution does not convey any benefits. Hence water was used as perfusate for development of online microdialysis-mass spectrometry. The online system took around one minute to equilibrate to step-changes in concentration and had detection limits around 0.5 μmol L−1 for alanine. Addition of isotope labelled alanine to soils led to an almost instantaneous increase and subsequent decrease in dialysate alanine concentration. With sterile soils there was a slow abiotic decrease in dialysate concentrations, presumably due to development of a depletion shell around the microdialysis probe and adsorption of alanine to the soil. For non-sterile soils there was an additional more rapid biotic decrease in dialysate concentrations that presumably reflected microbial uptake. For l-alanine added to non-sterile soil much of the compound was taken up before it reached the probe surface and concentrations decreased to below detection limits within 5–20 min. Thus microdialysis afforded a graphic illustration of the ephemeral nature of intact l-alanine in non-sterile soil, while parallel measurements showed that added d-alanine was removed from soil solution several times more slowly.

Carbon dioxide consumption of the microalga Scenedesmus obtusiusculus under transient inlet CO2 concentration variations.

The extensive microalgae diversity offers considerable versatility for a wide range of biotechnological applications in environmental and production processes. Microalgal cultivation is based on CO2 fixation via photosynthesis and, consequently, it is necessary to evaluate, in a short time and reliable way, the effect of the CO2 gas concentration on the consumption rate and establish the tolerance range of different strains and the amount of inorganic carbon that can be incorporated into biomass in order to establish the potential for industrial scale application. Dynamic experiments allow calculating the short-term microalgal photosynthetic activity of strains in photobioreactors. In this paper, the effect of step-changes in CO2 concentration fed to a 20L bubble column photobioreactor on the CO2 consumption rate of Scenedesmus obtusiusculus was evaluated at different operation times. The highest apparent CO2 consumption rate (336μmolm-2s-1 and 5.6% of CO2) was 6530mgCO2gb-1d-1 and it decreased to 222mgCO2gb-1d-1 when biomass concentration increased of 0.5 to 3.1gbL-1 and 5.6% of CO2 was fed. For low CO2 concentrations (<3.8%) the pH remained close to the optimal value (7.5 and 8). The CO2 consumption rates show that S. obtusiusculus was not limited by CO2 availability for concentrations above of 3.8%. The CO2 mass balance showed that 90% of the C-CO2 transferred was used for S. obtusiusculus growth.

The Detection Properties Comparison for the SnO2 Gas Sensor in Different Heating Regimes and the Step Change in Concentration

Non-periodical heating regimes and also periodical heating regimes were applied for the sensors TGS 813 and SP 11. Ethanol vapour in air was used as a detected substance. It was found that the sensitivity is better in the periodical square-wave heating regime among the tested regimes. The stabilisation of the sensor conductivity, when the concentration abruptly varies its value, takes longer compared to the constant heating regime at maximum heating voltage.

Spatial model of convective solute transport in brain extracellular space does not support a "glymphatic" mechanism.

A "glymphatic system," which involves convective fluid transport from para-arterial to paravenous cerebrospinal fluid through brain extracellular space (ECS), has been proposed to account for solute clearance in brain, and aquaporin-4 water channels in astrocyte endfeet may have a role in this process. Here, we investigate the major predictions of the glymphatic mechanism by modeling diffusive and convective transport in brain ECS and by solving the Navier-Stokes and convection-diffusion equations, using realistic ECS geometry for short-range transport between para-arterial and paravenous spaces. Major model parameters include para-arterial and paravenous pressures, ECS volume fraction, solute diffusion coefficient, and astrocyte foot-process water permeability. The model predicts solute accumulation and clearance from the ECS after a step change in solute concentration in para-arterial fluid. The principal and robust conclusions of the model are as follows: (a) significant convective transport requires a sustained pressure difference of several mmHg between the para-arterial and paravenous fluid and is not affected by pulsatile pressure fluctuations; (b) astrocyte endfoot water permeability does not substantially alter the rate of convective transport in ECS as the resistance to flow across endfeet is far greater than in the gaps surrounding them; and (c) diffusion (without convection) in the ECS is adequate to account for experimental transport studies in brain parenchyma. Therefore, our modeling results do not support a physiologically important role for local parenchymal convective flow in solute transport through brain ECS.

Methods of the gas concentration sinusoidal and step changes generation for dynamic properties of gas concentration meters testing

The generation methods of a gas concentration sinusoidal and step changes for dynamic properties assessment of the fast gas concentration meters are described. The need of such fast measurements occurs together with the rising scientists’ interest in contaminants and microorganisms dispersion in the air, especially during the tests of the risk of infection. While the laboratory tests are performed, the tracer gas instead of a infected air is used. Due to the high selectivity, good long-term stability and a wide measurement range, the infrared absorption method for measuring the gas concentration is used. The dynamic properties of this method are limited by the need of the exchange of the gas sample in the measuring chamber. Both constructed generators allow to obtain gas concentration changes with specified amplitude and frequency. The results of step and sinusoidal tests of selected CO2 concentration meter were compared and they showed a good agreement.

Effects of shear on P-selectin deposition in microfluidic channels.

Traditional leukocyte adhesion assays have provided significant insight into the mechanisms of leukocyte rolling in part through the use of homogeneously coated surfaces. These assays typically involve protein coating of glass coverslips or plastic petri dishes applied via a static drop of protein solution. With this approach, it is difficult to spatially control the location of proteins to fabricate surface-bound protein gradients that mimic in vivo situations. Microfluidic patterning of proteins with microfluidic devices has become a popular technique due to the ability to spatially pattern proteins on a cellular scale. Despite the advantages of microfluidic patterning, few studies have systematically investigated the effects of perfusion time, protein concentration, and perfusion shear stress on protein deposition. Herein, we demonstrated the fabrication of both line and step gradients of P-selectin on glass substrates that support cell rolling and adhesion assays. Investigation of the flow conditions during the microfluidic patterning led to several significant findings. We observed that the protein deposition time of 5 min was sufficient to deposit adequate P-selectin to support neutrophil rolling. We demonstrated that the amount of membrane P-selectin (mP-selectin) or recombinant P-selectin (rP-selectin) deposited showed a dependence on the perfusion shear stress between 4.0 and 32.0 dyn/cm(2), while similar studies with fibronectin or fibrinogen showed no shear stress dependence. Finally, we also created step changes in surface adherent protein concentration of P-selectin to characterize leukocyte-rolling behavior in response to sudden changes in ligand density.